Colorless volatile imaging liquids have been used for some time to develop a temporary image which then disappears when the imaging fluid evaporates. Volatile imaging liquids thereby permit the substrate to be used over and over again. In the bingo industry it is desirable that the volatile imaging liquid evaporate in less than four hours so that the bingo cards are ready to be played again.
One method of developing a temporary image is by using transparentizing fluids which fill microvoids in a substrate or substrate coating material. Reusable sheet materials using a micro-porous layer and a transparentizing fluid are discussed in a number of patents. For example, U.S. Pat. No. 4,299,880 to Arens discloses a microvoid-containing sheet material that is capable of displaying indicia when contacted with the appropriate colorless volatizing liquid and which is sufficiently durable that it cannot readily be transparentized by the application of heat or pressure. At least one surface of the reusable sheet material is coated with an opaque microporous layer comprising particles having a refractive index in the range of about 1.3 to 2.2, preferably about 1.4 to 1.8. The particles are incorporated in a binder which has a refractive index in the same range as the particles, interconnected microvoids being present throughout the layer and being open to the exposed surface of the sheet material. When liquid having a refractive index approximating that of the particles and the binder is applied to the microporous surface layer, the liquid penetrates the microvoids in the layer, thereby reducing its reflectivity in the intermediate vicinity of such penetration, imparting transparency and visually exposing the underlying surface of the base. Other examples of the use of transparentizing fluids and microporous sheet materials are discussed in U.S. Pat. Nos. 4,418,098; 4,729,687; 4,428,321; and 4,877,253.
Such microporous sheets are particularly attractive for use with reusable bingo cards as evidenced by U.S. Pat. No. 4,877,253. The bingo industry has substantially replaced markers that can be accidentally moved, such as chips, with colored ink markers. Applicators used to form these markers are commonly referred to as "dabbers", "markers" or "daubers". Dabbers that apply permanent colored ink are messy and lead to substantial waste since the card can be used only once. Alternately, the dabbers can be used to dispense a clear, volatile imaging liquid which forms a temporary marking image by imparting a transparentizing effect appearance when applied to the top surface of a microporous sheet bingo card. When the imaging liquid evaporates the bingo card returns to its normal appearance so that it can be used several times.
However, it is still a fairly common practice in bingo parlors today to provide players with conventional bingo cards or "tear opens" which are meant to be permanently marked and as such these cards are often permanently marked using a traditional colored ink marker and thus are good for only one game. Alternatively, U.S. Pat. No. 3,826,499 discloses an invisible printing ink which leaves a permanent mark on a bingo card when the invisible ink is chemically reacted with a marking pen. The invisible ink is a suitable acid or base material which is applied to the top surface of the bingo card and when the marking pen is applied the ink changes color via a chemical reaction and becomes visible.
Because games requiring a permanent image are often played concurrently with games using the more modern bingo cards in combination with a volatile liquid marking dabber, there is a substantial inconvenience and expense in having to use two different marking dabbers. It is therefore desirable to provide a marking system whereby a single marker may be used to form a temporary mark on one substrate, and a permanent mark on a second substrate.